Conventionally, as disclosed in Japanese Patent Laid-Open No. 2005-110202 (JP '202), a vehicle periphery monitoring apparatus having a wide-angle lens camera is proposed for providing a driver of a subject vehicle with a wider field of view, which has a view angle of at least 180 degrees. Though such an apparatus has a very wide view angle, a trade-off of having a smaller image size for an object captured in a corner/periphery of a captured image cannot be avoided. More practically, when a vehicle backs up, the driver of the subject vehicle, even though staring at the captured image of a rear view of the vehicle, cannot notice/recognize an object captured in the corner of the captured image that is very small, since the driver's attention is naturally drawn to a nearby vehicle parking on the left/right of the subject vehicle with minimum clearance.
Therefore, for example, a monitoring apparatus that emphasizes a moving object on a display unit is proposed in Japanese Patent Laid-Open No. 2005-123968 (JP '968), which emphasizes the moving object after cropping such object from the captured image. In JP '968, the emphasizing scheme of the moving object is disclosed as a calculation of an optical flow of feature points in the captured image and a formation of a motion vector for each of the feature points, enabling a cropping of the moving object from the captured image. The cropped moving object in a dead angle of the subject vehicle is then displayed in an emphasized manner on the display unit, thereby allowing the driver of the subject vehicle to easily notice/recognize such a dangerous object in the dead angle.
However, extraction of the motion vectors from the captured image by processing an image based on a calculation of the optical flow, as provided in JP '968, requires a huge processing load. Thus, an accurate cropping in response to the motion of the moving object may only be enabled by a separate/dedicated processor for having processing results in a timely manner.
Therefore, as shown in FIG. 7, in some recently-developed image capturing apparatus, a detection line L extending horizontally in a left-to-right axis is set in the captured image for capturing an outside periphery of the subject vehicle for the detection of the moving object. A detection area for detecting the moving object is narrowed to such detection line L. In particular, the brightness of a pixel along the detection line L changes according to a movement of the moving object.
By pre-defining a parameter representing a pixel along the detection line L, parametric detection of the brightness change of the pixel along the detection line L is enabled for detecting a moving object. Based on a comparison between a parametric definition of pixel's brightness, which serves as a template, and an actually-detected brightness of the pixel that has changed brightness along the detection line, the detection of the moving object is enabled.
However, even when the moving object is moving at a constant speed, the size of the brightness change or the number of pixels that have changed brightness and the amount of movement of such pixels per unit time (i.e., the movement speed) due to the movement of the moving object along the detection line L are different and depend on the position of such movement in the captured image.
FIGS. 8A and 8B show a captured image by using the wide-angle lens camera, in which an automotive vehicle is traveling from the right side toward the center of the captured image. In FIG. 8A, the vehicle is small in the right corner of the captured image. In FIG. 8B, the vehicle is large at the center of the captured image. Further, the amount of movement of the changing pixel per unit time is greater at the center of the captured image than at the right corner of the image.
However, in the apparatus of JP '968, the parameter representing the brightness change of the pixels along the detection line L (FIG. 7) is defined uniformly for the entire detection line L. Therefore, the apparatus can not accurately detect the moving object in the captured image.